The invention concerns a method for controlling an internal combustion engine, said internal combustion engine acting via a variable transmission, particularly a continuously variable transmission, on drivable wheels or the like of a motor vehicle, together with a drive arrangement, particularly for a motor vehicle, comprising an internal combustion engine operatively connected via a variable transmission, particularly a continuously variable transmission, to drivable wheels or the like.
Known from EP 0 451 887 B1, for example, is an electronically controlled continuously variable transmission whose gear ratio can be varied by means of an open-loop electronic controller. The gear ratio is adjusted in dependence on driver intention, which can be detected, for example, from the instantaneous position of the accelerator pedal. The gear ratio of the transmission can be adjusted with a view toward driving performance and/or fuel economy.
It is further known to control internal combustion engines via electronic controllers; torque-influencing variables of the internal combustion engine can be controlled in this case. This approach includes the control of a fuel injection system. It is known to at least reduce or, where appropriate, completely suspend fuel injection in order to reduce pollutant emissions and fuel consumption. The internal combustion engine then operates in what is known as overrun mode.
The present invention comprises, in one form thereof, a method for controlling an internal combustion engine which acts via a variable transmission, particularly a continuously variable transmission, on drivable wheels or the like of a motor vehicle, a fuel feed to the internal combustion engine being at least reduced in dependence on an operating state and the internal combustion engine operating in overrun mode and a gear ratio of the transmission being adjusted independently of driver intention in dependence on at least one operating parameter of the motor vehicle wherein during the overrun operation of the internal combustion engine (12), the gear ratio is controlled in such a way as to maximize the time interval for which the internal combustion engine (12) operates in the overrun operating state. The present invention comprises, in another form thereof, a drive arrangement particularly for a motor vehicle which includes an internal combustion engine that is operatively connected via a variable transmission, particularly a continuously variable transmission, to drivable wheels (22) or the like, and means via which a gear ratio of the transmission (16) is controlled in such a way that an overrun operating state of the internal combustion engine (12) can be made to last for a maximal time interval. These two forms of the invention offer the advantage that additional fuel economization and additional reduction of pollutant emissions can be achieved through engine control. Controlling the gear ratio during overrun operation of the internal combustion engine in such a way as to maximize the time interval for which the engine operates in the overrun operating state advantageously makes it feasible to affect the duration of overrun operation of the internal combustion engine via the transmission control system. In particular, if the starting rotation speed (the crankshaft rotation speed) of the internal combustion engine, that is, the crankshaft of the internal combustion engine, is adjusted via the gear ratio in such a way that the engine control system recognizes that the engine is in the overrun operating state, the engine control system can postpone the resumption of fuel injection to a later time if this accords with instantaneous driver intention. This prolongs the engine""s overrun cutoff phase, resulting in reduced fuel demand and thus reduced pollutant emissions because of this prolongation.
In a preferred embodiment of the invention, it is provided that the gear ratio is controlled in such a way that the crankshaft rotation speed of the engine is above a presettable threshold value that preferably corresponds to the current resumption rotation speed for fuel injection to the engine. Thus, advantageously, the input rotation speed (primary rotation speed) of the transmission and consequently the crankshaft rotation speed of the engine can be regulated to a given, selectable rotation speed value by simple control of the continuously variable transmission. In this way, depending on the instantaneous torque demand on the engine, which corresponds to driver intention, the crankshaft rotation speed of the engine can be kept above the resumption rotation speed for a maximum possible time interval via control of the transmission. This extends the operation of the engine in the overrun operating state to the maximum possible time interval, thus making it possible to maximize the fuel savings and the reduction of pollutant emissions that are associated with overrun operation of the engine.
In addition, the drive arrangement of the invention may include an internal combustion engine having output rotation speed that is increased to no more than the resumption rotation speed plus a presettable offset when in an overrun operating state thereby offering the advantage of enabling the prolongation of the overrun cutoff phase of the engine to be implemented in motor vehicles in a simple manner. Providing means for controlling a gear ratio of the transmission in such a way that an overrun operating state of the engine can be made to last for a maximum possible time interval advantageously makes it feasible to affect the overrun cutoff phase of the engine through simple transmission control means. In a preferred embodiment of the invention, these control means can be integrated into an electronic transmission controller.
Further preferred embodiments of the invention will become apparent from the other features recited in the dependent claims.